Video: The linear Box Blur

I am still looking at the Angry blocks. psd image. All I have done so far is to select this top layer 1 TL for top left, and apply the Gaussian Blur filter with a Radius of 16 pixels. Now Gaussian Blur employed a Gaussian bell-shaped curve in order to distribute its blurriness, so it blurs very slowly at the beginning, rapidly in the middle and slowly again at the end. And it's continuous. In other words it's a gentle curving slope of blurriness. So there are no corners in the blur.

Photoshop is one of the world’s most powerful image editors, and it can be daunting to try to use skillfully. Photoshop CS4 One-on-One: Advanced, the second part of the popular and comprehensive series, follows internationally renowned Photoshop guru Deke McClelland as he dives into the workings of Photoshop. He explores such digital-age wonders as the Levels and Curves commands, edge-detection filters, advanced compositing techniques, vector-based text, the Liquify filter, and Camera Raw. Deke also teaches tried-and-true methods for sharpening details, smoothing over wrinkles and imperfections, and enhancing colors without harming the original image. Exercise files accompany the course.

The linear Box Blur

I am still looking at the Angry blocks. psd image. All I have done so far is toselect this top layer 1 TL for top left, and apply the Gaussian Blur filterwith a Radius of 16 pixels. Now Gaussian Blur employed a Gaussian bell-shapedcurve in order to distribute its blurriness, so it blurs very slowly at thebeginning, rapidly in the middle and slowly again at the end. And it'scontinuous. In other words it's a gentle curving slope of blurriness. So thereare no corners in the blur.

Whereas if it did not employ that approach if it just went ahead and blurredeverything by the same amount regardless of the luminance level then we wouldend up with edges after our blur and I'll show you what that looks like. I'mgoing to switch to the 2 TR layer right there. So second top right and I'll goup to the Filter menu and I'll choose Blur and I'll choose this guy right hereBox Blur which is the Linear Blur function inside of Photoshop.Interestingly, Gaussian Blur, the more sophisticated command has been with usforever inside the program. Box Blur just came about a few years ago inPhotoshop CS2.

All right, so I'm going to choose the Box Blur command, and right now it lookslike just a typical Blur function at this low Radius value, at least it's a lowRadius value for me, it might be higher for you by default. And I'm going tocrank that up rather than sort of wandering through our Radius values. Sonotice by the way we have to work with integers, so no decimals here inside ofthis dialog box.So pressing the Up Arrow key raises the value in even number of pixels rightthere and whole pixels. I'm going to take this value up to 16, however it mightas well just cut to the chase and click OK. So we are matching the same Radiusvalue that we employed with the Gaussian Blur filter, but notice that we get avery different effect with edges inside of it.

So much of the geometry of this original object is still intact. You can makeout that sort of cyborg face in the background. And you can see thisreally distinct edge right in this area, right there. And that would normallybe a bad thing. If we were employing a Box Blur for Drop Shadow for example,which you can't do, but if that was the way it worked then we would get thesevery harsh edges at the end of our drop shadows and that's why otherapplications that apply drop shadows and have these weird edges on them, that'swhy they get them is because they don't do the mathematics properly. They justgo ahead and blur everything by the same amount. Photoshop gets it right withthe Gaussian Blur as you can see.

But if for some reason you want to retain the geometry of an object as you blurit then Box Blur is going to be the better way to go and does end producing aboxy effect as you can see here. You can kind of see this little corner outhere that's being described by the blurry corner of that rectangular outline.And notice that it is going ahead in blurring both the image and thetransparency mask associated with this layer, just as before if we didn't wantto blur the transparency mask, and of course we could lock down our transparency.All right, so that's it. That's Box Blur for you. In the next exercise we aregoing to move for a moment from blurring to averaging as we take a look at theMedian and Dust and Scratches commands.

Learn by watching, listening, and doing, Exercise files are the same files the author uses in the course, so you can download them and follow along Premium memberships include access to all exercise files in the library.

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Learn by watching, listening, and doing! Exercise files are the same files the author uses in the course, so you can download them and follow along. Exercise files are available with all Premium memberships.
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